The present invention relates generally to a bicycle gearshifting mechanism, and more particularly to a bicycle speed-changing mechanism making use of only one sleeve and a plurality of control slot sets to carry out a power source impartation. The mechanism also makes use of another sleeve and another control slot to control the one-way ratchet pawl so as to control the fastening of the sun gear set.
The inner speed changing mechanism of the conventional bicycle has a planetary gear mechanism which is provided with the input member, which may be a ring gear or gear support. The ring gear or gear support is engaged with the toothed portion of a clutch for controlling the path of the power input of the planetary gear mechanism so as to control the degrees of freedom of the sun gear, thereby resulting in various speed ratios. In accordance with the characteristic of the planetary gear mechanism, the rotational direction of the sun gear is related to the driving power input member of the gear train. In other words, when the transmission is carried out by various power input members (gear support or ring gear), the rotational direction of the sun gear is changed. If the gear support is used as a driving power member, the sun gear is identical in the rotational direction to the gear support. If the ring gear is used as the driving power member, the rotational direction of the sun gear is opposite to the rotational direction of the ring gear. In order to resolve such a motion characteristic of the planetary gear train, the U.S. Pat. No. 5,399,128 discloses a sun gear which is provided in the inner edge thereof with a plurality of retaining slots. The sun gear is retained by a control key. However, the control key may fail to enter the retaining slot at the time when the speed ratio is changed. In keeping with such a principle, the disclosure makes use of the power input member to bring about the shifting process, which is by no mends free from troubles.
With the view of controlling the degrees of freedom of the sun gear, the U.S. Pat. No. 5,322,487 discloses two sets of two-step planetary gear for controlling the degrees of freedom of the sun gear in conjunction with two rotary sleeves and the projection on the fastening shaft. The expected speed ratio is thus attained. However, such an increase in number of the planetary gear and the sun gear results in a substantial increase in weight and complexity of the whole mechanism.
It is therefore the primary objective of the present invention to provide a speed-changing control mechanism of the multistage speed-changing wheel hub, which is capable of controlling smoothly the fastening mechanism of the sun gear.
It is another objective of the present invention to provide a speed-changing control mechanism of the multistage speed-changing wheel hub, which is capable of controlling smoothly the shifting of the power input member.
The foregoing objectives, features, functions, and advantages of the present invention will be more readily understood upon a thoughtful deliberation of the following detailed description of a preferred embodiment of the present invention with reference to the accompanying drawings.